Method of evaluating optical information medium

ABSTRACT

A method for transferring an artificial fingerprint liquid to a surface of an optical information medium includes preparing a pseudo-fingerprint transferring stamp which is a plug made of silicone rubber, applying an artificial fingerprint liquid containing a fine-particle-form substance and a dispersion medium capable of dispersing the fine-particle-form substance onto a polycarbonate substrate by spin coating to prepare a master plate for artificial fingerprint liquid transfer, pressing said one end face of the transferring stamp with a load of 4.9 N for 10 seconds against the surface of the master plate, and then, pressing said one end face of the transferring stamp onto which the artificial fingerprint liquid is transferred against a surface of an optical information medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/074,762, filed Mar. 9, 2005, which is a continuation application ofPCT/JP2004/003221, filed Mar. 11, 2004, which was published under PCTArticle 21(2) in Japanese, which claims priority to Japanese ApplicationNo. 2003-074553, filed Mar. 18, 2003, the entire contents of each ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method for evaluating an opticalinformation medium, and more specifically, to a simple method forevaluating an optical information medium by judging the surface qualityof the medium by the use of a novel artificial fingerprint liquid as anevaluation dispersion liquid.

BACKGROUND ART

When an optical disk such as a reproduction-only optical disk, opticalrecording disk, magneto-optical recording disk, and the like, is used,the adhesion of stains or fingerprints to the surface thereof is causedon the basis of various stain materials. The adhesion of these stains orfingerprints is unpreferable, and in some cases, the surface of theoptical disk is subjected to an appropriate surface treatment in orderto improve an anti-staining property thereof, decrease a fingerprintadhering property or improve a fingerprint removing property.

For example, investigations are being made on various water repellent oroil repellent treatments to the surface of the optical disk. In order tocheck the effect of improving the anti-staining property by the surfacetreatments, in many cases, there is used a manner of adhering afingerprint actually onto the optical disk surface and, then, evaluatingthe wiping-off property thereof with the naked eye. However, such anevaluating manner is poor in quantitativeness and reproducibility.

On the assumption that if the water repellency or the oil repellency ofthe optical disk surface is high, stain materials are easily removed,the following is frequently performed: measurement of the contact anglesof various liquids, such as water and aliphatic hydrocarbons, to theabove treated-surface. However, the evaluation based on the contactangle or surface free energy is, in a sense, an indirect evaluatingmanner. Accordingly, it can be properly used as a manner for evaluatingthe anti-staining property in only a highly restricted case where theabove-mentioned assumption that if the water repellency or the oilrepellency is high, excellent anti-staining property is exhibited comesinto effect. This evaluating manner gives only a relative evaluationresult at best. In other words, when this evaluating manner is appliedto an optical disk surface, it is substantially impossible that athreshold value which represents whether or not the disk can be usedwithout causing any practical problem is determined for the contactangle or surface free energy.

In recent years, it has been desired that about optical informationmedia the recording density thereof is made higher in order to store amass of data such as moving image data. Thus, researches anddevelopments are being actively made for making the density of recordingcapacity higher. As one of them, the following suggestion is made: asseen in, for example, a DVD, the recording/reproducing wavelengththereof is made short and the numerical aperture (NA) of the objectivelens is made large, thereby making the condensed spot diameter of thereproducing/reproducing beam small. As compared with a CD, a recordingcapacity (4.7 GB/surface) 6 to 8 times that of the CD is actuallyattained by changing the recording/reproducing wavelength from 780 nm to650 nm and changing the numerical aperture (NA) from 0.45 to 0.60.Recently, as a method for recording high-quality moving images for along time, an attempt has been made to make the recording/reproducingwavelength short up to about 400 nm and making the numerical aperturehigh up to 0.85, so as to attain a recording capacity 4 times or morethat of DVD.

However, when the recording density is made high in this way, thecondensed spot diameter of the recording/reproducing beam becomes small.Consequently, the recording medium-becomes more sensitive to dust, dirt,fingerprints or the like adhering to the laser beam incident sidesurface of the medium than the conventional art. In particular, aboutstains containing an organic material, such as fingerprints, a largeeffect is produced when the stains adhere to the laser beamincident-side surface. Since the stains are not easily removed, manycountermeasures have been considered so far.

For example, Japanese Laid-open Patent Publication Nos. 10-110118 (1998)and 11-293159 (1999) suggest that when a hard coat agent coated film isformed on a surface of an optical disk substrate made of polycarbonateor the like, a non-crosslinking type fluorine type surfactant isincorporated into the hard coat agent. In order to evaluate theanti-staining property of the hard coat surface of the optical disk,there is performed an operation of adhering an artificial fingerprintliquid wherein a small amount of sodium chloride, urea and lactic acidis dissolved in a mixture solution of water and ethanol onto the surfaceof the hard coat under pressure, using a pseudo fingerprint, and thendetermining the wiping-off property thereof with the naked eye. Thisartificial fingerprint liquid is a liquid described in JIS K2246: 1994“Rust Preventing Oil”. The JIS standard prescribes a performance-testingmethod for rust preventing oils used for temporary rust-prevention ofmetal materials such as steel. Accordingly, the artificial fingerprintliquid is prepared to determine the corrosiveness of metal materials.For this reason, the liquid is not useful at all for purposes other thanthis. Even if the artificial fingerprint liquid made mainly of water andethanol is adhered onto a surface of an optical disk substrate made ofresin such as polycarbonate, in reality the artificial fingerprintliquid is repelled and is not fixed on the substrate surface in almostall cases. It can be considered from this fact that the resin substratesurface exhibits the same wiping-off property against the artificialfingerprint liquid whether the surface is not subjected to any surfacetreatment or is subjected to surface treatment. That is, it is hardlysignificant to use the artificial fingerprint liquid prescribed in LISK2246: 1994 for evaluation of the anti-staining property or thefingerprint removing property of an optical disk surface.

From such an actual-situation, it is desired to develop an artificialfingerprint liquid for quantitatively and with a good reproducibilityevaluating the surface quality of an optical disk. It is also desired todevelop a simple evaluating method for quantitatively and reproduciblyjudging the surface quality of an optical disk by the use of theartificial fingerprint liquid.

DISCLOSURE OF THE INVENTION Objects of the Invention

Thus, an object of the present invention is to solve the above-mentionedproblems of the conventional art and provide a simple method forevaluating an optical information medium by judging quantitatively andreproducibly the surface quality of the optical information medium bythe use of a novel artificial fingerprint liquid as an evaluationdispersion liquid.

SUMMARY OF THE INVENTION

The present invention comprises the following inventions.

(1) A method for evaluating an optical information medium, comprisingthe steps of:

adhering, under predetermined conditions, an evaluation dispersionliquid containing a fine-particle-form substance and a dispersion mediumcapable of dispersing the fine-particle-form substance onto the surfaceof the optical information medium which is on the incident side of arecording and/or reproducing beam;

measuring an area ratio of the medium surface occupied with theevaluation dispersion liquid droplets adhered per unit area of themedium surface; and

judging the optical information medium as an acceptable medium when themeasured area ratio is 6% or less.

(2) A method for evaluating an optical information medium, comprisingthe steps of:

adhering, under predetermined conditions, an evaluation dispersionliquid containing a fine-particle-form substance and a dispersion mediumcapable of dispersing the fine-particle-form substance onto the surfaceof the optical information medium which is on the incident side of arecording and/or reproducing beam;

measuring a recording and/or reproducing characteristic of the mediumwith the evaluation dispersion liquid droplets adhered to the mediumsurface; and

judging the optical information medium as an acceptable medium when themeasured recording and/or reproducing characteristic is equal to, orbetter than, a predetermined value.

(3) A method for evaluating an optical information medium, comprisingthe steps of:

adhering, under predetermined conditions, an evaluation dispersionliquid containing a fine-particle-form substance and a dispersion mediumcapable of dispersing the fine-particle-form substance onto the surfaceof the optical information medium which is on the incident side of arecording and/or reproducing beam;

measuring the error rate as a recording and/or reproducingcharacteristic of the medium, with the evaluation dispersion liquiddroplets adhered to the medium surface; and

judging the optical information medium as an acceptable medium when themeasured error rate is equal to, or smaller than, a predetermined value.

(4) The method for evaluating an optical information medium according toany one of the above (1) to (3), wherein the fine-particle-formsubstance contained in the evaluation dispersion liquid has an averageparticle size of 0.05 μm or more and 30 μm or less.

(5) The method for evaluating an optical information medium according toany one of the above (1) to (4), which is applied to the opticalinformation medium intended for use in a system wherein the smallestdiameter of the recording and/or reproducing beam on the surface whichis on the incident side of the recording and/or reproducing beam is 500μm or less.

(6) The method for evaluating an optical information medium according toany one of the above (1) to (4), which is applied to the opticalinformation medium intended for use in a system wherein the smallestdiameter of the recording and/or reproducing beam on the surface whichis on the incident side of the recording and/or reproducing beam isgreater than 500 μm.

The present invention provides a simple method for evaluating an opticalinformation medium such as a reproduction-only optical disk, opticalrecording disk, magneto-optical recording disk, and the like, by judgingquantitatively and reproducibly the quality of the recording/reproducingbeam incident side surface of the optical information medium by the useof a novel artificial fingerprint liquid as an evaluation dispersionliquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a structuralexample of an optical information medium.

FIG. 2 is a schematic cross-sectional view illustrating anotherstructural example of the optical information medium.

FIG. 3 is a schematic cross-sectional view of an optical recording disksample used in Example.

FIG. 4 is a schematic cross-sectional view of an optical recording disksample used in Example.

MODES FOR CARRYING OUT THE INVENTION

First, a novel artificial fingerprint liquid used as an evaluationdispersion liquid in the present invention is described.

The artificial fingerprint liquid used in the present inventioncomprises a fine-particle-form substance and a dispersion medium capableof dispersing the fine-particle-form substance. In the presentdescription, the term “dispersion medium” refers only to a liquidcomponent that remains as a pseudo-fingerprint component after theartificial fingerprint liquid has been transferred to the surface of anoptical information medium to be evaluated, but not to a diluent that isoptionally used when using the artificial fingerprint liquid, and ismostly or completely evaporated finally after the transfer of theartificial fingerprint liquid.

The dispersion medium preferably has a surface tension ranging from 20to 50 mNm⁻¹ at 25° C. By such a constituent, the artificial fingerprintliquid is made up to an artificial fingerprint liquid having a characteras close as possible to an actual fingerprint. Thus, the artificialfingerprint liquid can be suitably used for evaluating an anti-stainingproperty, a fingerprint adhering property, or a fingerprint removingproperty on the surface of an optical disk to be evaluated.

In the case that an artificial fingerprint liquid of a homogeneouscomponent system made only of a liquid is used at this time, the liquiddoes not approximate to the removing property of any actual fingerprint.For example, in the case that triolein, which is one ofsebum-constituting components, is used as the homogeneous system, thesurface tension of triolein is 34 mNm⁻¹ at 25° C. Therefore, the surfaceof polytetrafluoroethylene (PTFE), which has a critical surface tensionof about 18 mNm⁻¹, repels triolein completely without getting wet.However, actual fingerprints never fail to be fixed even on the PTFEsurface. This is mainly because any fingerprint is not made only of aliquid substance but is made of a heterogeneous system containing aninsoluble material and a viscous material. Accordingly, by making aheterogeneous system wherein an appropriate insoluble component is addedto a dispersion medium made of a liquid component contained in an actualfingerprint and/or a liquid similar thereto, the artificial fingerprintliquid having a character as close as possible to an actual fingerprintcan be obtained.

Herein, critical surface tension will be described. The water repellencyand the oil repellency of a material can be represented into one way bycritical surface tension (γ_(c)/mNm⁻¹), which is a criterion of thesurface free energy of the material. The critical surface tension can beobtained from an actually-measured value of the contact angle thereof.Specifically, the contact angle (θ/rad) to a smooth surface made of aspecified material is measured about several saturated hydrocarbonliquids each having a known surface tension (surface tension: γ₁/mNm⁻¹).A value extrapolated to cos θ=1 in plots of cos θ and γ₁ is the criticalsurface tension γ_(c) of the specified material. In order that somematerial can repel a liquid, it is necessary that the critical surfacetension γ_(c) of the material is less than the surface tension γ₁ of theliquid. For example, γ_(c) of a material having a surface composition ofa methylene chain (—CH₂—)_(n) is 31 mNm⁻¹. Accordingly, the materialrepels water, which has a surface tension γ₁ of 73 mNm⁻¹ at atemperature of 20° C., but completely gets wet to n-hexadecane, whichhas a surface tension γ₁ of 28 mNM⁻¹. The contact angle thereof turns to0 degree.

The artificial fingerprint liquid used in the present inventioncomprises a fine-particle-form substance in the dispersion medium. Themajority of solid components contained in any actual fingerprint is aprotein called keratin. In the simplest way, therefore, fine powders ofkeratin are added to and mixed with the dispersion medium having theabove physical property values, so that the above-mentioned artificialfingerprint liquid can be prepared. Indeed, a mixture wherein keratinfine powders are mixed with a dispersion medium, such as water, oleicacid, squalane or triolein, at an appropriate ratio can be effectivelyused as the artificial fingerprint liquid of the present invention.However, generally available keratin is remarkably expensive. Thus, alarge amount thereof cannot be easily obtained. Furthermore,commercially available keratin has a different particle sizedistribution from that of keratin contained in actual fingerprints. Itis therefore necessary to adjust the particle size distribution thereofin advance if necessary. Accordingly, it cannot be necessarily said thatthe method of using commercially available keratin is a preferablemethod from the viewpoint of simplicity, measurement precision and itsreproducibility.

In order to solve the problems of keratin, the present inventorsresearched a fine-particle-form substance which can be used instead ofkeratin. As a result, it has been found that fine particles having agood wettability to the dispersion medium having the above physicalproperty values and having particle sizes close to that of keratincontained in actual fingerprint components are preferable as thefine-particle-form substance.

The artificial fingerprint liquid used in the present invention includesat least one selected from inorganic fine particles and organic fineparticles as the fine-particle-form substance. The inorganic fineparticles, which are not particularly limited, may be, for example,silica fine particles, alumina fine particles, iron oxide fineparticles, and mixtures of any two or more selected from the fineparticles. The organic fine particles, which are not particularlylimited, may be, for example, chitin fine particles, chitosan fineparticles, acrylic type fine particles, styrene type fine particles,divinylbenzene type fine particles, polyamide type fine particles,polyimide type fine particles, polyurethane type fine particles,melamine type fine particles, and mixtures of any two or more selectedfrom the fine particles.

All of the inorganic fine particles exhibit, as the constitutingcomponent of the artificial fingerprint liquid, the same effect askeratin fine particles, and are further more inexpensive than thekeratin fine particles. Therefore, in order to decrease costs and makethe performance stable, the content of the inorganic fine particles ispreferably 50% by weight or more, more preferably 80% by weight or more,and considerably preferably 100% by weight of the whole of thefine-particle-form substance. It is advisable that organic fineparticles may be used together if necessary. Among the organic fineparticles, acrylic type fine particles, styrene type fine particles,divinylbenzene type fine particles, polyamide type fine particles,polyimide type fine particles, polyurethane type fine particles,melamine type fine particles and the like are preferable since they arerelatively inexpensive. Further, keratin fine particles may be usedtogether.

The fine-particle-form substance preferably has an average particle size(that is, median diameter) of 100 μm or less, and more preferably has anaverage particle size of 50 μm or less. Examples of thefine-particle-form substance which includes an inorganic component andhas an average particle size of 100 μm or less include JIS Z8901 testingpowders 1 and 2, ISO testing powder 12103-1, and the Association ofPowder Process Industry and Engineering Japan (APPIE) standard powder.All the testing powders are preferable since they have uniform particlesizes and are available at a relatively low cost. Among examples of theJIS Z8901 testing powder 1, Kanto loam is preferable. It is allowable touse, besides the respective testing powders per se, at least one ofinorganic fine particles contained in the respective testing powders,for example, at least one selected from various oxide fine particlessuch as SiO₂, Fe₂O₃ and Al₂O₃. The average particle size of thefine-particle-form substance is preferably 0.05 μm or more, morepreferably 0.5 μm or more. Accordingly, the average particle size of thefine-particle-form substance is preferably 0.05 μm or more and 30 μm orless, more preferably 0.5 μm or more and 10 μm or less. If thefine-particle-form substance is too large or too small, the substratecannot exhibit easily a sufficient function as an alternate material ofkeratin contained in actual fingerprints.

The fine-particle-form substance preferably has a critical surfacetension at 25° C. larger than that of the used dispersion medium at 25°C., and the critical surface tension is preferably 40 mNm⁻¹ or more,more preferably 50 mNm⁻¹ or more. All of the above particles exemplifiedas the inorganic fine particles have such a desired nature about thecritical surface tension.

In the present invention, as the dispersion medium, there is preferablyused a liquid having a surface tension ranging from 20 to 50 mNm⁻¹ at25° C. and a saturated vapor pressure of 760 mmHg (101325 Pa) or less at200° C. The liquid which constitutes sweat or sebum of human beings or aliquid having a character close to it usually has such physical propertyvalues. Accordingly, it is advisable to use a liquid having the physicalproperty values as the dispersion medium of the artificial fingerprintliquid in the present invention. If the surface tension is less than 20mNm⁻¹ at 25° C., the wettability to the surface of an optical disk to beevaluated becomes too high, so that the artificial fingerprint liquidadheres far more easily onto the optical disk surface and is moredifficultly removed than actual fingerprints. On the other hand, if thesurface tension exceeds 50 μl at 25° C., the wettability to the opticaldisk surface to be evaluated lowers, so that the artificial fingerprintliquid adheres far more difficultly onto the optical disk surface and ismore easily removed than actual fingerprints.

If the saturated vapor pressure exceeds 760 mmHg (101325 Pa) at 200° C.,the dispersion medium volatilizes gradually after the adhesion of thefingerprint onto the optical disk surface to be evaluated, so that thestate of the adhering artificial fingerprint may change in a short time.What degree of easiness of the volatilization of the dispersion mediumis after the adhesion of the fingerprint onto the optical disk surfaceto be evaluated is also affected by the temperature of the optical disksurface to be evaluated, the temperature of the use environment of theartificial fingerprint liquid, or the like.

In the present invention, it is desirable that the viscosity of theliquid used as the dispersion medium is preferably 500 cP or less, morepreferably from 0.5 to 300 cP, and still preferably from 5 to 250 cP at25° C. By having such a viscosity, the dispersion medium causes thefine-particle-form substance to be satisfactorily dispersed and beeasily fixed to the optical disk surface even after the adhesion of thefingerprint onto the optical disk surface to be evaluated.

The dispersion medium is not particularly limited, and examples thereofinclude higher fatty acid, derivatives of higher fatty acid, terpenes,and derivatives of terpenes. Examples of the higher fatty acid includevarious acids such as oleic acid, linoleic acid, linolenic acid. Thederivatives of higher fatty acid may be ester derivatives, and examplesthereof include diglyceride derivatives and triglyceride derivatives(for example, triolein). The terpenes may be various terpenes, andexamples thereof include squalane, limonene, α-pinene, β-pinene,camphene, linalool, terpineol, andcadinene. It is advisable to select atleast one from these and use the selected one alone or the selected twoor more in a mixture form. It is also preferable to mix one or morethereof with water and use the mixture.

In the present invention, an appropriate mixing ratio between thefine-particle-form substance and the dispersion medium depends on themethod of adhering the artificial fingerprint liquid onto the opticaldisk surface to evaluated, which method will be described later, andothers. Therefore, the mixing ratio cannot be specified withoutreservation. In general, however, 0.1 to 5.0 weights of thefine-particle-form substance are preferably added per weight of thedispersion medium, and 0.1 to 3.0 weights of the fine-particle-formsubstance are more preferably added, and 0.2 to 1.0 weights of thefine-particle-form substance are most preferably added. If the mixingratio of the fine-particle-form substance to the dispersion medium istoo low or too high, it becomes difficult that the resultant functionseffectively as an artificial fingerprint liquid. If thefine-particle-form substance is at a ratio less than 0.1, the effect ofthe addition of the fine-particle-form substance is not obtained, sothat the artificial fingerprint liquid is not easily fixed on theoptical disk surface to be evaluated or the liquid tends to be easilyremoved even if the liquid is fixed. On the other hand, if thefine-particle-form substance is added at a ratio over 5.0, liquidcrosslinking effect, based on the dispersion medium, on the optical disksurface to evaluated deteriorates, so that the artificial fingerprintliquid tends not to be easily fixed.

As mentioned above, the dispersion medium refers only to a liquidcomponent that remains as a pseudo-fingerprint component after theartificial fingerprint liquid has been transferred to the optical disksurface to be evaluated, but not to a diluent which is described later.

In the present invention, it is also preferable to add a wax, that is,an ester of higher fatty acid and monovalent alcohol to these dispersionmedium components, which are liquid at ambient temperature, so as tomake the viscosity of the dispersion medium components high. As the wax,for example, the following may be used: a natural wax such as candelillawax, carnauba wax, urucury wax, rice wax, sugar wax, wood wax, beeswax,spermaceti, Chinese insect wax, shellac wax, or montan wax; or asynthetic wax such as cholesteryl stearate, myristyl myristate, or cetylpalmitate. The addition percentage of each of the waxes may beappropriately determined in accordance with the property of the opticaldisk to be evaluated, for example, the property of therecording/reproducing optical system of the optical disk, the purpose ofthe evaluation, and others.

A general thickener may be added to the artificial fingerprint liquid,examples thereof including carrageenan, gum arabic, xanthan gum,galactomannan, and pectin. Furthermore, in order to improve thedispersibility of the fine-particle-form substance, various surfactantsmay be added, examples thereof including quaternary ammonium salts,alkylbenzenesulfonates, and polyoxyethylene polyoxypropylene glycol.

In the present invention, the artificial fingerprint liquid may bediluted with a diluent such as isopropyl alcohol, methyl ethyl ketone ormethoxypropanol if necessary in order to improve the transferringproperty of the artificial fingerprint. These diluents are mostly orcompletely evaporated finally after the transfer of the artificialfingerprint liquid to the optical disk surface to be evaluated. Thediluent usually has a saturated vapor pressure exceeding 760 mmHg(101325 Pa) at 200° C. It is allowable to add ethanol, liquid paraffinor the like appropriately to the artificial fingerprint liquid.

In a way as described above, the artificial fingerprint liquid used inthe present invention is composed.

A method is next described for transferring the artificial fingerprintliquid as the evaluation-dispersion liquid onto therecording/reproducing beam incident side surface of the optical disk tobe evaluated, under predetermined conditions, to form apseudo-fingerprint.

In the present invention, when the artificial fingerprint liquid isadhered to the surface of the optical information medium to beevaluated, under predetermined conditions, it is preferable to use apseudo-fingerprint transferring stamp made of elastomer. Specifically,it is preferable to produce a pseudo-fingerprint transferring stamp madeof silicone rubber, butadiene rubber, urethane rubber or the like anduse this. The pseudo-fingerprint transferring stamp may be made intosuch a shape that a fingerprint pattern is precisely copied from a moldwhich is actually obtained from man's fingers. In a simpler way, it ispreferable to use a rubber plug for printing an artificial fingerprintliquid prescribed in JIS K2246-1994. That is, it is possible to use, asthe pseudo-fingerprint transferring stamp, a material the surface ofwhich is roughened by polishing a small circular surface (diameter:about 26 mm) of a No. 10 rubber plug with an AA240 abrasive materialprescribed in JIS R6251 or JIS R6252 or a abrasive material havingperformance similar thereto. However, without limitation to theabove-mentioned material, a material capable of giving substantially thesame pseudo-fingerprint transferring property as described above can bepreferably used. In order to obtain a size close to that of an actualfingerprint, an object having a smaller diameter than theabove-mentioned rubber plug is preferably used. Specifically, a rubberplug having a diameter of 8 to 25 mm is preferably used, and a rubberplug having a diameter of 8 to 20 mm is more preferably used.

The method of using such a pseudo-fingerprint transferring stamp totransfer the artificial fingerprint liquid, as a pseudo fingerprint,onto an optical disk surface under predetermined conditions, can beappropriately determined in accordance with the purpose of theevaluation. For example, a master plate for pseudo-fingerprint patterntransfer is previously produced, and the rubber plug is used to transfera pseudo-fingerprint from this master plate onto the optical disksurface to be evaluated. Specifically, the artificial fingerprint liquidis uniformly applied onto a rigid substrate made of glass or resin. Asthe coating method at this time, an appropriate method may be used fromvarious coating methods such as spin coating and dip coating methods.When the artificial fingerprint liquid is applied onto the substrate,the liquid may be diluted with an appropriate organic solvent such asisopropyl alcohol or methyl ethyl ketone in order to obtain a goodapplication property. It is advisable to evaporate these diluents by airdrying or heat drying after the application. In this way, the substrateonto which the artificial fingerprint liquid is uniformly applied isproduced and this is used as a master plate for pseudo-fingerprintpattern transfer.

Under predetermined conditions, the artificial fingerprint liquid istransferred as a pseudo-fingerprint from the master plate forpseudo-fingerprint pattern transfer onto the surface of an optical diskto be evaluated by means of the pseudo-fingerprint transferring stamp.Procedures to carry out the transfer process are properly determineddepending on the level of the surface characteristics required of theoptical disk to be evaluated (i.e., anti-staining property, fingerprintadhering property, or fingerprint removing property), and/or thecomponents and compositions of the artificial fingerprint liquid used.While such transfer procedures are not limited to particular procedures,independent procedures as described in the following Levels 1 through 4may be used:

Level 1:

1. Transfer the artificial fingerprint liquid material applied to thesurface of the master plate onto the pseudo-fingerprint transferringstamp by pressing the transferring stamp against the surface of themaster plate on which the artificial fingerprint liquid is applied,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are properlydetermined.

2. Subsequently, transfer the pseudo-fingerprint pattern onto thesurface of the optical disk to be evaluated by pressing the transferringstamp with the artificial fingerprint liquid material transferred on itagainst the surface of the optical disk, under a predetermined load of 1N to 35 N for a predetermined period of time. The load and the time overwhich the load is applied are also properly determined.

Level 2:

1. Transfer the artificial fingerprint liquid material applied to thesurface of the master plate onto the pseudo-fingerprint transferringstamp by pressing the transferring stamp against the surface of themaster plate on which the artificial fingerprint liquid is applied,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are properlydetermined.

2. Subsequently, transfer a portion of the transferred artificialfingerprint liquid material onto the transferring stamp, onto thesurface of a polycarbonate substrate (e.g., polycarbonate substrate thathas an identical shape to the optical disk to be evaluated) by pressingthe transferring stamp with the transferred artificial fingerprintliquid material against the surface of the polycarbonate substrate,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are alsoproperly determined.

3. Subsequently, transfer the pseudo-fingerprint pattern onto thesurface of the optical disk to be evaluated by pressing the transferringstamp, on which a portion of the artificial fingerprint liquid materialhas removed off, against the surface of the optical disk, under apredetermined load of 1 N to 35 N for a predetermined period of time.The load and the time over which the load is applied are also properlydetermined.

Level 3:

1. Transfer the artificial fingerprint liquid material applied to thesurface of the master plate onto the pseudo-fingerprint transferringstamp by pressing the transferring stamp against the surface of themaster plate on which the artificial fingerprint liquid is applied,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are properlydetermined.

2. Subsequently, transfer a portion of the transferred artificialfingerprint liquid material onto the transferring stamp, onto thesurface of a polycarbonate substrate (e.g., polycarbonate substrate thathas an identical shape to the optical disk to be evaluated) by pressingthe transferring stamp with the transferred artificial fingerprintliquid material against the surface of the polycarbonate substrate,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are alsoproperly determined.

3. Subsequently, further transfer an additional portion of theartificial fingerprint liquid material on the transferring stamp onto adifferent area of the surface of the polycarbonate substrate by pressingagain the transferring stamp, on which a portion of the artificialfingerprint liquid material has removed off, against the different areaof the surface of the polycarbonate substrate, under a predeterminedload of 1 N to 35 N for a predetermined period of time. The load and thetime over which the load is applied are also properly determined.

4. Subsequently, transfer the pseudo-fingerprint pattern onto thesurface of the optical disk to be evaluated by pressing the transferringstamp, on which a portion of the artificial fingerprint liquid materialhas removed off twice, against the surface of the optical disk, under apredetermined load of 1 N to 35 N for a predetermined period of time.The load and the time over which the load is applied are also properlydetermined.

Level 4:

1. Transfer the artificial fingerprint liquid material applied to thesurface of the master plate onto the pseudo-fingerprint transferringstamp by pressing the transferring stamp against the surface of themaster plate on which the artificial fingerprint liquid is applied,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are properlydetermined.

2. Subsequently, transfer a portion of the transferred artificialfingerprint liquid material onto the transferring stamp, onto thesurface of a polycarbonate substrate (e.g., polycarbonate substrate thathas an identical shape to the optical disk to be evaluated) by pressingthe transferring stamp with the transferred artificial fingerprintliquid material against the surface of the polycarbonate substrate,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are alsoproperly determined.

3. Subsequently, further transfer an additional portion of theartificial fingerprint liquid material on the transferring stamp onto adifferent area of the surface of the polycarbonate substrate by pressingagain the transferring stamp, on which a portion of the artificialfingerprint liquid material has removed off, against the different areaof the surface of the polycarbonate substrate, under a predeterminedload of 1 N to 35 N for a predetermined period of time. The load and thetime over which the load is applied are also properly determined.

4. Repeat the procedure 3 above.

5. Subsequently, transfer the pseudo-fingerprint pattern onto thesurface of the optical disk to be evaluated by pressing the transferringstamp, on which a portion of the artificial fingerprint liquid materialhas removed off three times, against the surface of the optical disk,under a predetermined load of 1 N to 35 N for a predetermined period oftime. The load and the time over which the load is applied are alsoproperly determined.

As the level of the transfer process increases from the above-describedlevel 1 to level 4, the amount of the artificial fingerprint liquidtransferred to the surface of the optical disk to be evaluated decreasescorrespondingly. When it is desired to determine the characteristicquality of the optical disk by a decreased amount of the fingerprintliquid adhered to the disk surface, the level of the transfer processmay be raised.

In the present invention, the artificial fingerprint liquid ispreferably a liquid obtained by: adding a diluent selected fromisopropyl alcohol, methyl ethyl ketone and methoxypropanol to a mixtureof Kanto loam having an average particle size of 0.5 μm or more and 10μm or less (JIS Z8901 testing powder) as the fine-particle-formsubstance and triolein in a weight ratio of Kanto loam to triolein of0.2 to 1.0.

In the present invention, the transferring stamp is preferably a productobtained by rubbing the circular surface of rubber plug having adiameter of 8 to 20 mm with an AA240 abrasive material prescribed in JISR6251 or JIS R6252, or with an equivalent abrasive material to make thesurface rough.

The use of the above-described method makes it possible that theartificial fingerprint liquid is adhered onto the recording/reproducingbeam incident side surface of the optical disk with a goodreproducibility.

As an observing index of the state of the artificial fingerprint liquiddroplets adhered under predetermined conditions onto therecording/reproducing beam incident side surface of the optical disk, inthe present invention, an area ratio of the disk surface occupied withthe artificial-fingerprint liquid droplets adhered per unit area of thedisk surface is measured. However, indices other than the area ratio,such as the diameter, the perimeter, the relationship between theperimeter and the area (i.e., degree of roundness), the absolute maximumlength, the aspect ratio, the number, the distance between centers ofgravity, and the area distribution of area ratio of the artificialfingerprint liquid droplets adhered onto the disk surface may also used.Furthermore, the maximum value, the minimum value, the mean value, thetotal value, the proportion, and the standard deviation of droplets maybe suitably used for each of these indices.

(Evaluation by Measuring the Area Ratio of the Disk Surface Occupiedwith the Artificial Fingerprint Liquid Droplets Adhered Per Unit Area ofthe Disk Surface)

In the present invention, as described above, the artificial fingerprintliquid is adhered, under predetermined conditions, onto therecording/reproducing beam incident side surface of an optical disk. Andthen, the area ratio of the disk surface occupied with the artificialfingerprint liquid droplets adhered per unit area of the disk surface ismeasured. The optical disk is judged as an acceptable disk when themeasured area ratio is 6% or less.

The state of the droplets of the artificial fingerprint liquid adheredto the surface of the optical disk is observed with an opticalmicroscope, and its images are processed on a computer to determine thearea ratio of the disk surface occupied with the artificial fingerprintliquid droplets using image-processing technology. Usingimage-processing technology, the area ratio can be obtained simply bydividing the artificial fingerprint liquid droplets-adhered portion anddroplets-free portion into 2-value, measuring respective areas.

Considering the spot size of laser beam, the artificial fingerprintliquid droplets less than 5 μm in diameter adhered to the disk surfaceare considered to hardly affect the focusing and trackingcharacteristics of laser beam. Therefore, in measurement of focusing andtracking characteristics, the artificial fingerprint liquid dropletsless than 5 μm in diameter may be ignored for the convenience (namely,considered as the artificial fingerprint liquid droplets-free portion)to effect the above measurement. However, in measurement of recordingand/or reproducing signals such as error rates, even such smallartificial fingerprint liquid droplets can affect the measurement. Thus,the artificial fingerprint liquid droplets less than 5 μm in diametershould be taken into account in measuring these signals. As used herein,“the diameter of the artificial fingerprint liquid droplet” isdetermined by measuring the area of the artificial fingerprint liquiddroplet adhered to the disk surface, assuming that each artificialfingerprint liquid droplet is a perfect circle, and calculating thediameter of the perfect circle from the area of individual droplet.

In case of using an artificial fingerprint liquid described in Examples,it has been demonstrated that when the area ratio of the disk surfaceoccupied with the artificial fingerprint liquid droplets exceeds 6%, theerror rate becomes unfavorable. Thus, for evaluation of an opticalinformation medium, the optical information medium in which this arearatio is 6% or less may be judged as an acceptable medium. Further, forsafety, a specific area ratio value smaller than 6% may be suitablydetermined, the optical information medium having the area ratio notmore than the specific area ratio value may be judged as an acceptablemedium. For example, in case the medium having the area ratio not morethan 1% is judged as an acceptable medium, only the medium having thevery favorable error rate can be judged as an acceptable medium.

(Evaluation by Measuring the Recording and/or Reproducing Characteristicof Optical Disk with the Artificial Fingerprint Liquid Droplets Adheredto the Disk Surface)

And, in the present invention, as described above, the artificialfingerprint liquid is adhered, under predetermined conditions, onto therecording/reproducing beam incident side surface of an optical disk. Andthen, the recording and/or reproducing characteristic of the opticaldisk is measured with the artificial fingerprint liquid droplets adheredto the surface. The optical disk is judged as an acceptable disk whenthe measured recording and/or reproducing characteristic is equal to, orbetter than, a predetermined value. The predetermined value of therecording/reproducing characteristic may be suitably determined based onthe performance level required of the optical disk to be evaluated.

The recording/reproducing characteristic to be measured is notparticularly limited, and examples thereof include reflectance, degreeof modulation, and RF signals flatness during the reproducing process ofthe medium; jitter, output level, carrier-to-noise ratio (CN ratio), anderror rate of any of recorded signals, erasable signals, andnon-erasable signals; and peak-to-peak (p-p) value of afocus/sensitivity curve obtained for the line speed during the recordingor reproducing process, the amount of residual error of focus errorsignals, and the ratio of the p-p value to the residual error. One ormore of these characteristics may be measured as the standard forevaluation. The focus/sensitivity curve assumes what is commonly knownas a sigmoid curve and is described in page 81 of “Optical diskTechnology” published on Feb. 10th, 1988, by Radio Technology Co., Ltd.From the focus/sensitivity curve, the p-p value of the focus errorsignals output, namely the difference between the peak value of positiveoutput and the peak value of negative output is obtained to berepresented as “F”. On the other hand, the output p-p value of theresidual error of focus error signals is obtained to be represented as“R”. If the value R/F is small, specifically 10% or less, then thejitter generated during the reproducing process becomes sufficientlysmall and writing errors are significantly reduced.

(Evaluation by Measuring the Error Rate of Optical Disk with theArtificial Fingerprint Liquid Droplets Adhered to the Disk Surface)

In the present invention, as described above, the error rate can bemeasured as the recording and/or reproducing characteristic of anoptical disk. Namely, the evaluation dispersion liquid, which contains afine-particle-form substance and a dispersion medium capable ofdispersing the fine-particle-form substance, is adhered, underpredetermined conditions, onto the recording/reproducing beam incidentside surface of an optical information medium. And then, the error rateas a recording and/or reproducing characteristic of the medium ismeasured, with the evaluation dispersion liquid droplets adhered to themedium surface. The optical information medium is judged as anacceptable medium when the measured error rate is equal to, or smallerthan, a predetermined value. The term “error rate” refers to known errorrates such as bit-by-bit error rate and symbol error rate. Thepredetermined value for the error rate may be suitably determined basedon the performance level required of the optical disk to be evaluated.In general, bit-by-bit error rate or symbol error rate of 10⁻⁴ orsmaller are small enough for practical use.

Further, in evaluation of optical disk surface, the artificialfingerprint liquid may be transferred to the surface of a data-recordedoptical disk and the data is subsequently read out, or alternatively,the artificial fingerprint liquid may be transferred to the surface ofan unrecorded optical disk and the data is subsequently recorded andread out.

The evaluation method of the present invention is applied to evaluatethe surface quality of the optical disk such as a reproduction-onlyoptical disk, optical recording disk, magneto-optical recording disk,and the like, and is preferably applied to the optical informationmedium intended for use in a system wherein the smallest diameter of therecording/reproducing beam on the surface which is on the incident sideof the recording/reproducing beam is 500 μm or less. As for such anoptical information medium, if fingerprints or other stains are adheredon the recording/reproducing beam incident side surface of the mediumduring use of the medium, deterioration problem of recording and/orreproducing characteristics, such as error rates is particularly liableto occur.

Needless to say, the evaluation method of the present invention is alsoapplicable to the optical information medium intended for use in asystem wherein the smallest diameter of the recording/reproducing beamon the surface which is on the incident side of therecording/reproducing beam is greater than 500 μm.

A structural example of an optical information medium to which thepresent invention is applied is shown in FIG. 1. This opticalinformation medium is a recording medium, and comprises a recordinglayer (4) that functions as an information recording layer on asupporting substrate (20) of comparatively high rigidity, alight-transmitting layer (7) on the recording layer (4), and a lighttransmitting hard coat layer (8) on the light-transmitting layer (7).The hard coat layer (8) acts as the surface upon which therecording/reproducing beam is incident, and the laser beam for recordingor reproducing is incident through the hard coat layer (8) and thelight-transmitting layer (7), and onto the recording layer (4). Thethickness of the light-transmitting layer (7), including the hard coatlayer (8), is preferably within a range from 30 to 300 μm, and even morepreferably from 70 to 150 μm. A thin anti-staining surface layer thatshows a high water repellency and a high oil repellency may be furtherformed on the hard coat layer (8).

Influence, based on adhesion of a fingerprint, on recording/reproducingproperty depends on the diameter of a laser beam (the smallest diameterin the case that the beam section is elliptic) on the medium surfacewhich is on the incident side of the laser beam. When this diameter issmall, large influences as follows are produced: continuous errors,which cannot be corrected, are made. The present inventors' research hasdemonstrated that in the case that the diameter of the laser beamincident side surface of the medium is 500 μm or less, in particular,300 μm or less, bad influence on the recording/reproducing propertybecomes remarkable when a fingerprint adheres to the medium which isbeing handled. The diameter of the laser beam, on the laser beamincident side surface of the medium, is represented as follows:2t·tan{sin⁻¹(NA/n)}wherein the thickness of the light-transmitting layer (7) in FIG. 1 isrepresented by t, the refractive index of the light-transmitting layer(7) is represented by n, and the numerical aperture of the objectivelens of the recording/reproducing optical system is represented by NA.It should be noted that in this term, the hard coat layer is neglectedsince the difference in refractive index between the hard coat layer (8)and the light-transmitting layer (7) is small enough and the hard coatlayer (8) is significantly thinner than the light-transmitting layer(7).

The present invention can be applied regardless of the kind of therecording layer. That is, the present invention can be applied to arecording medium whether the medium is, for example, a phase-change typerecording medium, a bit-forming type recording medium or amagneto-optical recording medium. Usually, a dielectric layer or areflective layer for protecting the recording layer or attaining anoptical effect is laid on at least one side of the recording layer.However, the above laid layer is not shown in FIG. 1. The presentinvention can be applied to a reproduction-only type, as well as arecordable type as illustrated. In this case, a pit row integrated withthe supporting substrate (20) is formed, and a reflective layer (metallayer or dielectric multilayered film) covering the pit row constitutesan information recording layer.

The present invention can also be applied to an optical informationmedium of a structural example shown in FIG. 2. The medium illustratedin FIG. 2 comprises an information recording layer (4) on one surface ofa light transmitting, supporting substrate (20), and a protective layer(6) on the information recording layer (4), whereas a light-transmittinghard coat layer (8) is formed on the other surface of the supportingsubstrate (20). The hard coat layer (8) acts as the surface upon whichthe recording/reproducing beam is incident, and the laser beam forrecording or reproducing is incident through the hard coat layer (8) andthe supporting substrate (20), and onto the recording layer (4).

The two media each having the structure illustrated in FIG. 1 or FIG. 2are adhered to each other so as to cause the hard coat layers (8) toface outwards, so that a two-sided recording type medium can beproduced.

EXAMPLES

The present invention will be more specifically described by way of thefollowing examples. However, the present invention is not limited tothese examples.

[Production of Disk Sample A]

An optical recording disk sample A with the layer structure shown inFIG. 3 was produced. In FIG. 3, the optical disk A has a supportingsubstrate (20) having information pits, pregrooves, and other fine scaleconcavities-convexities formed on one surface thereof. On this surface,the optical disk has a reflective layer (3), a second dielectric layer(52), a recording layer (4), and a first dielectric layer (51) formed inthis order, and further has a light-transmitting layer (7) on the firstdielectric layer (51), and a hard coat layer (8) on the lighttransmitting layer (7). When using the optical disk (1), a laser beamfor recording or reproducing is incident through the hard coat layer (8)and the light transmitting layer (7).

Using a disk shaped supporting substrate (20) (formed frompolycarbonate, diameter 120 mm, thickness 1.1 mm) in which informationrecording grooves had been formed, sputtering was used to form areflective layer (3) of thickness 100 nm comprising Al₉₈Pd₁Cu₁ (atomicratio) on the groove-side surface of the substrate. The depth of thegrooves, which is represented by light-path length at a wavelength λ=405nm, was set into λ/6. The recording track pitch in the groove-recordingscheme was set into 0.3 μm.

Subsequently, sputtering with an Al₂O₃ target was used to form a seconddielectric layer (52) of thickness 20 nm on the surface of thereflective layer (3). Sputtering using an alloy target comprising aphase-changing material was then used to form a recording layer (4) ofthickness 12 nm on the surface of the second dielectric layer (52). Thecomposition (atomic ratio) of the recording layer (4) wasSb₇₄Te₁₈(Ge₇In₁). Sputtering with a ZnS (80 mol %)-SiO₂ (20 mol %)target was then used to form a first dielectric layer (51) of thickness130 nm on the surface of the recording layer (4).

Subsequently, a radical polymerizable, ultraviolet ray-curable materialwith the composition shown below was applied onto the surface of thefirst dielectric layer (51) by spin coating, and was then irradiatedwith ultraviolet rays, thus forming a light transmitting layer (7) witha cured thickness of 98 μm. (Light transmitting layer: composition ofthe ultraviolet ray-curable material) Urethane acrylate oligomer 50parts by weight (Diabeam UK6035, manufactured by Mitsubishi Rayon Co.,Ltd.) Isocyanuric acid EO modified triacrylate 10 parts by weight(Aronix M315, manufactured by Toagosei Co, Ltd.) Isocyanuric acid EOmodified diacrylate 5 parts by weight (Aronix M215, manufactured byToagosei Co., Ltd.) Tetrahydrofurfuryl acrylate 25 parts by weightPhotopolymerization initiator 3 parts by weight (1-hydroxycyclohexylphenyl ketone)

Subsequently, an ultraviolet ray/electron ray-curable hard coat agentwith the composition shown below was applied onto the light transmittinglayer (7) by spin coating to form a coating layer, and the appliedcoating layer was then heated at 60° C. for 3 minutes in an atmosphereto remove the diluent in the coating layer. And then, the coating layerwas irradiated with ultraviolet rays to form the hard coat layer (8)having a cured thickness of 2 μm. In this manner, the disk sample A wasprepared. (Composition of the hard coat agent) Reactive group modifiedcolloidal silica 100 parts by weight (dispersion medium:propyleneglycomonomethyl- ether acetate, nonvolatile content: 40% byweight) Dipentaerythritol hexaacrylate 48 parts by weightTetrahydrofurfuryl acrylate 12 parts by weight Propyleneglycolmonomethylether acetate 40 parts by weight (unreactive diluent) IRGACURE184 (polymerization initiator) 5 parts by weight Bifunctional siliconemethacrylate 0.25 part by weight (X-22-164A, manufactured by Shin-EtsuChemical Co., Ltd.)[Production of Disk Sample B]

An optical recording disk sample B with the layer structure shown inFIG. 4 was produced. The optical disk B of FIG. 4 further includes ananti-staining surface layer (9) on the hard coat layer (8) of theoptical disk A of FIG. 3. When using the optical disk B, a laser beamfor recording or reproducing is incident through the anti-stainingsurface layer (9), the hard coat layer (8) and the light transmittinglayer (7).

The same procedures were followed as in the production of the opticaldisk A up to the formation of the light transmitting layer (7).

An ultraviolet ray/electron ray-curable hard coat agent with thecomposition shown below was applied onto the light transmitting layer(7) by spin coating to form a coating layer, and the applied coatinglayer was then heated at 60° C. for 3 minutes in an atmosphere to removethe diluent in the coating layer. And then, the coating layer wasirradiated with ultraviolet rays to form the hard coat layer (8) havinga cured thickness of 2 μm. (Composition of the hard coat agent) Reactivegroup modified colloidal silica 100 parts by weight (dispersion medium:propyleneglycolmono- methylether acetate, nonvolatile content: 40% byweight) Dipentaerythritol hexaacrylate 48 parts by weightTetrahydrofurfuryl acrylate 12 parts by weight Propyleneglycolmonomethylether acetate 40 parts by weight (unreactive diluent) IRGACURE184 (polymerization initiator) 5 parts by weight

Further, an ultraviolet ray/electron ray-curable fluorine-containinganti-staining agent with the composition shown below was applied ontothe hard coat layer (8) by spin coating to form a coating layer, and theapplied coating layer was then heated at 60° C. for 3 minutes in anatmosphere to remove the diluent in the coating layer. And then, thecoating layer was irradiated with electron electron rays to form theanti-staining surface layer (9) having a cured thickness ofapproximately 30 nm. In this manner, the disk sample B was prepared.(Composition of the anti-staining agent) Perfluoropolyether diacrylate 1part by weight (An acrylate-modified product of Fomblin ZDOL,manufactured by Ausimont Co., Ltd., Molecular Weight: about 2,000)3-perfluorooctyl-2-hydroxypropylacrylate 3 parts by weight (R-1833,manufactured by Daikin Fine Chemical Laboratory Co., Ltd.)Fluorine-containing solvent 1600 parts by weight (FLUORINERT FC-77,manufactured by Sumitomo 3M Co., Ltd.)[Preparation of Artificial Fingerprint Liquid and Adhesion to the DiskSamples](Preparation of Artificial Fingerprint Liquid)

0.4 parts by weight of Kanto loam of class 11 testing powder 1 (mediandiameter: 1.6 to 2.3 μm) prescribed in JIS Z8901 as thefine-particle-form substance, 1 part by weight of triolein as thedispersion medium, and 10 parts by weight of methoxypropanol as thediluent were mixed and stirred to form an artificial fingerprint liquid.

(Formation of Master Plate for Transferring Pseudo-Fingerprint Patterns)

A master plate for transferring pseudo-fingerprint patterns was producedas follows. While the artificial fingerprint liquid was sufficientlystirred with a magnetic stirrer, an approximately 1 mL portion of theliquid was collected. The collected liquid was applied onto apolycarbonate substrate (diameter: 120 mm, thickness: 1.2 mm) by spincoating. Spin coating was carried out at 500 rpm for 2 seconds, followedby 250 rpm for 2 seconds. This substrate was heated at 60° C. for 3minutes to completely remove methoxypropanol, which was the diluentwhich had become unnecessary. In this way, master plate for transferringpseudo-fingerprint patterns was obtained.

(Transfer of Pseudo-Fingerprint Patterns to the Surface of Disk Samples)

The artificial fingerprint liquid material was transferred onto thesurface of the hard coat layer (8) or the anti-staining surface layer(9) of the respective disk samples at the following adhesion levels 1through 4.

Adhesion Level 1:

A No. 1 silicone rubber plug was uniformly rubbed with a #240 abrasivepaper (having the equivalent performance to AA240 abrasive paperdescribed in the above JIS) on its smaller end surface (diameter: 12 mm)and was used as the pseudo-fingerprint transferring stamp. The rubbedend surface of the pseudo-fingerprint transferring stamp was pressedagainst the master plate with a load of 4.9 N for 10 seconds to transferthe artificial fingerprint liquid material to the end surface of thetransferring stamp. Subsequently, the end surface of the transferringstamp, onto which the artificial fingerprint liquid material adhered,was pressed against an area of the surface of the hard coat layer (8) orthe anti-staining surface layer (9) of the respective disk samples, thearea being located about 4.0 nm apart in the radius direction from thecenter the disk, with a load of 4.9 N for 10 seconds to transfer theartificial fingerprint liquid material.

Adhesion Level 2:

As in the Adhesion Level 1, the rubbed end surface of anotherpseudo-fingerprint transferring stamp was pressed against the masterplate with a load of 4.9 N for 10 seconds to transfer the artificialfingerprint material to the end surface of the transferring stamp.Subsequently, the end surface of the transferring stamp, onto which theartificial fingerprint liquid material adhered, was pressed against thesmooth surface of a polycarbonate substrate with a load of 4.9 N for 10seconds to reduce the adhesion amount of artificial fingerprint liquidmaterial on the end surface of the transferring stamp. The end surfaceof the transferring stamp, on which the adhesion amount was reduced, waspressed against an area of the surface of the hard coat layer (8) or theanti-staining surface layer (9) of the respective disk samples, the areabeing located about 40 mm apart in the radius direction from the centerthe disk, with a load of 4.9 N for 10 seconds to transfer the artificialfingerprint liquid material.

Adhesion Level 3:

The step taken in Adhesion Level 2 of reducing the adhesion amount wasrepeated twice by pressing the end surface of the transferring stamp,onto which the artificial fingerprint liquid material adhered, against apolycarbonate substrate twice successively with a load of 4.9 N for 10seconds but on separate locations on the polycarbonate substrate. Thisfurther reduced the adhesion amount of artificial fingerprint liquidmaterial on the end surface of the transferring stamp. The rest of theprocess was carried out in the same manner as in Adhesion Level 2 totransfer the artificial fingerprint liquid material onto the surface ofthe hard coat layer (8) or the anti-staining surface layer (9) of therespective disk samples.

Adhesion Level 4:

The step taken in Adhesion Level 2 of reducing the adhesion amount wasrepeated three times by pressing the end surface of the transferringstamp, onto which the artificial fingerprint liquid material adhered,against a polycarbonate substrate three times successively with a loadof 4.9 N for 10 seconds but on separate locations on the polycarbonatesubstrate. This further reduced the adhesion amount of artificialfingerprint liquid material on the end surface of the transferringstamp. The rest of the process was carried out in the same manner as inAdhesion Level 2 to transfer the artificial fingerprint liquid materialonto the surface of the hard coat layer (8) or the anti-staining surfacelayer (9) of the respective disk samples.

[Evaluation of Disk Samples]

(Measurement of the Area Ratio of the Surface Occupied with theArtificial Fingerprint Liquid Droplets Adhered Per Unit Area of theSurface)

The state of the droplets of the artificial fingerprint liquid adheredto the surface of each disk sample was observed with an opticalmicroscope (VK-8510, manufactured by Keyence Co., Ltd.). This image wasprinted on a printer (VH-P40, manufactured by Keyence Co., Ltd.). Andthe image was read and was processed on a computer to determine the arearatio of the surface area occupied with the artificial fingerprintliquid droplets to the whole surface area, by using animage-processing/analysis software Win ROOF, ver. 3.61 (Demonstrationversion, manufactured by Mitani Corporation). The analysis included theartificial fingerprint liquid droplets less than 5 μm in diameter.

(Measurement of Error Rate)

Information was recorded on each disk sample, and then the bit-by-biterror rate (bER) was measured on an evaluation apparatus for opticalrecording media (DDU-1000, manufactured by Pulstec Industrial Co., Ltd.,wavelength λ=405 nm, NA=0.85) to give an initial error rate. The disksample A had an initial error rate of 0, while the disk sample B had aninitial error rate of 1×10⁻⁷. Next, the artificial fingerprint liquiddroplets were adhered onto the surface of each disk sample at eachoperation of Adhesion Level 1 through Adhesion Level 4, and the errorrate (bER) was measured with the artificial fingerprint liquid dropletsadhered to the disk surface. 10 disk samples were used for each AdhesionLevel and the average value was determined.

The results of the above measurements are shown in Table 1 below. TABLE1 Disk A Disk B Level Area ratio Judgement bER Judgement Area ratioJudgement bER Judgement 1 10.8%  Defective 3 × 10⁻³ Defective 4.9%Acceptable 2 × 10⁻⁶ Acceptable 2 9.6% Defective 2 × 10⁻⁴ Defective 1.0%Acceptable 2 × 10⁻⁷ Acceptable 3 6.0% Acceptable 6 × 10⁻⁵ Acceptable0.9% Acceptable 1 × 10⁻⁶ Acceptable 4 5.2% Acceptable 7 × 10⁻⁶Acceptable 0.2% Acceptable 2 × 10⁻⁷ Acceptable

As can be seen from Table 1, when the transferring operation was carriedout using the same condition, less amounts of the artificial fingerprintliquid droplets adhered to the surface of the respective disk samples Bthan the amounts of the artificial fingerprint liquid droplets adheredto the corresponding disk samples A. This indicates that the disksamples B have a better anti-staining property than the disk samples A.

When the transferring operation was carried out at Adhesion Levels 1 and2, the area ratios of the surface area of the respective disk samples Aoccupied with the adhered artificial fingerprint liquid droplets were10.8% and 9.6%, each larger than 6.0%. Thus, each disk sample A wasjudged as defective. At the same Adhesion Levels, the area ratios of thesurface area of the respective disk samples B occupied with the adheredartificial fingerprint liquid droplets were 4.9% and 1.0%, each not morethan 6.0%. Thus, each disk sample B was judged as acceptable. When thetransferring operation was carried out at Adhesion Levels 3 and 4, thearea ratios of the surface area of the respective disk samples Aoccupied with the adhered artificial fingerprint liquid droplets were6.0% and 5.2%, each not more than 6.0%. Thus, each disk sample A wasjudged as acceptable. At the same Adhesion Levels, the area ratios ofthe surface area of the respective disk samples B occupied with theadhered artificial fingerprint liquid droplets were 0.9% and 0.2%, eachnot m-ore than 6.0%. Thus, each disk sample B was also judged asacceptable.

These results show that the conditions for transferring operation may besuitably determined based on the level of the surface performancerequired of an optical disk to be evaluated. That is, in case where theoptical disk is considered unacceptable even if it has as high a surfaceperformance as the disk sample A and is required to have a highersurface performance comparable to that of the disk sample B, by carryingout the transferring operation at Adhesion Levels 1 or 2, the disksamples A and B are respectively judged as defective and acceptable onthe basis of the difference between surface performances of both disksamples A and B. And, when an optical disk with as high a surfaceperformance as that of the disk sample A is considered as acceptable,the transferring operation may be carried out at Adhesion Levels 3 or 4.

The area ratio value of the surface occupied with the artificialfingerprint liquid droplets was correlated with the error rate valuemeasured with the artificial fingerprint liquid droplets adhered to thedisk surface. This clearly shows that the surface performance of anoptical disk can be evaluated by determining the error rate with theartificial fingerprint liquid droplets adhered to the disk surface,instead of determining the area ratio of the surface occupied with theartificial fingerprint liquid droplets. When the error rate is used inthe evaluation, a threshold value of error rate is suitablypredetermined based on the performance level required of an optical diskto be evaluated, and the optical disk is judged as acceptable if theerror rate is less than or equal to the threshold value. In the presentexamples, one example is described in which judgement of acceptable ordefective was carried out based on the threshold error rate value of1×10⁻⁴. In general, error rates of 1×10⁻⁴ or smaller are sufficient forpractical use.

As set forth, it has been demonstrated that the area ratio value of theartificial fingerprint liquid droplets, or the error rate value as therecording/reproducing characteristic can be used as a standard forjudging the quality of the optical disk. The components and compositionof the artificial fingerprint liquid (i.e., evaluation dispersionliquid), conditions for adhering the artificial fingerprint liquid, andthe predetermined values of recording/reproducing characteristics areappropriately determined based on the surface performance level requiredof an optical disk to be evaluated.

1. A method for transferring an artificial fingerprint liquid to asurface of an optical information medium, the method comprising:preparing a pseudo-fingerprint transferring stamp which is a plug madeof silicone rubber, and one end face of said plug being roughened bypolishing with an abrasive, applying an artificial fingerprint liquidcontaining a fine-particle-form substance and a dispersion mediumcapable of dispersing the fine-particle-form substance onto apolycarbonate substrate by spin coating to prepare a master plate forartificial fingerprint liquid transfer, pressing said one end face ofthe transferring stamp with a load of 4.9 N for 10 seconds against thesurface of the master plate onto which the artificial fingerprint liquidis applied, so as to transfer the artificial fingerprint liquid onto thetransferring stamp, and then, pressing said one end face of thetransferring stamp onto which the artificial fingerprint liquid istransferred against a surface of an optical information medium to beevaluated with a load of 4.9 N for 10 seconds, so as to transfer theartificial fingerprint liquid onto the surface of the medium.
 2. Themethod according to claim 1, wherein said one end face of thepseudo-fingerprint transferring stamp has a diameter of 8 to 25 mm. 3.The method according to claim 1, wherein said one end face of thepseudo-fingerprint transferring stamp is roughened by polishing with a#240 abrasive paper.
 4. The method according to claim 1, wherein theartificial fingerprint liquid contains Kanto loam of class 11 testpowder 1 prescribed in JIS Z8901 as the fine-particle-form substance,and triolein as the dispersion medium.
 5. The method according to claim1, wherein the artificial fingerprint liquid contains 0.4 parts byweight of Kanto loam of class 11 test powder 1 prescribed in JIS Z8901as the fine-particle-form substance, and 1 part by weight of triolein asthe dispersion medium.